As a reaction force mechanism for a backrest and for generating a force against the backrest of a reclining chair to try to push the backrest back to an original position, there is conventionally proposed a reaction force mechanism including a weight-dependent reaction force mechanism for generating a force for pushing back the backrest by lifting a seat in relation to the reclining of the backrest as well as a reaction force mechanism utilizing a spring (Patent Literatures 1 and 2).
As shown in FIG. 19, the weight-dependent reaction force mechanism in Patent Literature 1 includes: a base 102 supported on a leg 101; a back support rod 104 to which a backrest 103 is mounted; a seat support member 106 to which a seat 105 is mounted; a shaft 107 for coupling the back support rod 104 to the base 102 so that the back support rod 104 can recline; links 108 for coupling a front portion of the seat support member 106 to the base 102; and an extension portion 110 of the back support rod 104 coupled to a back portion of the seat support member 106 by a shaft 109. When the backrest 103 reclines, the extension portion 110 of the back support rod 104 and the standing links 108 lift the seat 105.
The weight-dependent reaction force mechanism in Patent Literature 2 has the same basic concept as Patent Literature 1 in which a large reaction force is generated abruptly in an initial stage of reclining of the backrest and then the reaction force reduces. To solve this problem of the invention in Patent Literature 1, instead of the links 108, elongate holes 200 and a shaft 201 are utilized to lift a front portion of a seat support member 202 diagonally backward and upward in relation to the reclining of a back support member 203 (see FIG. 20).
Here, in each of the reaction force mechanisms for the backrests in Patent Literatures 1 and 2, a reaction force spring 111 or 204 used together with the weight-dependent reaction force mechanism is disposed vertically while sandwiched between the back support member and the base member behind a rotation shaft (a shaft which serves as a fulcrum of the weight-dependent reaction force mechanism), which serves as a rotation center of the back support member. Accordingly, the reaction force spring 111 or 204 directly receives a swing of the back support member in a vertical direction to thereby generate the reaction force.